1. Field of the Invention
The present invention relates to a spread illuminating apparatus of side light type, particularly a spread illuminating apparatus including a transparent resin plate integrally composed of a light conductor plate portion and a housing frame portion, to a transparent resin plate for use in a spread illuminating apparatus, and further to a method of injection-molding such a transparent resin plate.
2. Description of the Related Art
A liquid crystal display (LCD) device is characterized by a small thickness, a small occupation volume, a light weight and the like and is used extensively in various electric products, such as a mobile telephone and a personal computer.
Since a liquid crystal in the LCD device does not emit light by itself, an illuminating means is required when the LCD device is used at a place where a solar light or an illumination light is not fully available.
While the LCD device is requested to be further downsized, its display area is requested to be enlarged. In order to satisfy such requests at one time, the ineffective portion of a lighting means must be reduced, and also its power consumption is desired to be lowered, which is achieved by efficiently utilizing light from a light source.
Under the circumstance where downsizing and power consumption reduction are requested, a point light source such as a light emitting diode (LED) is used as a light source for an illuminating means, and also constituent members of an illuminating means, such as a light source, a light conductor plate and the like are positioned in place to efficiently utilize light emitted from the light source.
FIG. 9 shows a relevant portion of a conventional spread illuminating apparatus in which a rectangular light conductor plate 1 and LEDs 2, 2 disposed at a side surface 8 of the light conductor plate 1 are disposed in place inside a housing frame 7 made of a white resin. Protrusions 12a and 12c are provided at each of side surfaces 11 and 12 of the light conductor plate 1 orthogonal to the side surface 8 having the LEDs 2, 2, and recesses 20a and 20c are provided at each of two inner side surfaces of the housing frame 7 opposing the side surfaces 11 and 12 of the light conductor plate 1, wherein the light conductor plate 1 is firmly held in place inside the housing frame 7 such that the protrusions 12a and 12c of the light conductor plate 12 engage respectively with the recesses 20a and 20c of the housing frame 7 (refer, for example, to Japanese Patent Application Laid-Open No. 2005-302485).
In the engagement structure described above, however, a predetermined gap is required between the side surface 11/12 of the light conductor plate 1 and the inner side surface of the housing frame 7, and light loss attributable to the gap must be made up for by some measures. The white resin of the housing frame 7 has a smaller reflectance than a reflection film to constitute a light reflecting sheet, such as an enhanced specular reflector (ESR) (refer, for example, to Japanese Patent Application published under No. H9-506837), and some action must be taken to make up for light loss attributable to this low reflectance.
When the apparatus described above is further reduced in thickness, its entire rigidity becomes insufficient, and also it is likely to happen that the protrusions 12a and 12c of the light conductor plate 1 disengage from the recesses 20a and 20c of the housing frame 7. FIG. 10 shows another conventional spread illuminating apparatus adapted to achieve a sufficient mechanical strength in the downsizing effort, which has an integrated structure of a light conductor plate portion 421 and a housing frame portion 422, where a pattern 426 is formed at a predetermined distance from light sources 410, 410 (refer, for example, to Japanese Patent Application Laid-Open No. 2006-285171).
In the integrated structure described above, however, the housing frame portion 422 is to be made of a resin material of which the light conductor plate portion 421 is also made and which has a high optical transmittance, and therefore light is caused to leak from the housing frame portion 422. In consideration of the light leakage problem, grooves 425 are provided at portions of the light conductor plate portion 421 located close to the housing frame portion 422, and light emitted from the light source 410 and traveling in the light conductor plate portion 421 is totally reflected by the grooves 425.
Since polycarbonate or polymethylmethacrylate that is a common resin material for a light conductor plate has a refractive index of about 1.5 and has a relatively large critical angle, it may potentially happen that lots of lights emitted from the light source 410 and traveling in the light conductor plate impinge on the grooves 425 at an angle smaller than the critical angle of the resin material depending on the design of constituent members, and that the grooves 425 fail to adequately prevent the lights from leaking thus causing light loss.
Also, for preventing light leakage from the housing frame portion 422, a reflective film must be fixedly attached to the outer side surfaces of the housing frame portion 422 by some kind of method, and, for example, if a double face tape is used for fixed attachment, light is absorbed by the adhesive layers of the double face tape. Even if the reflective film can be fixedly attached without using a double face tape, light is inevitably absorbed and lost to some extent while traveling in the housing frame portion 422.
Further, when such the integrated structure (resin plate) as described above is made by injection molding, in view of a gate cutting process, an injection gate for filling resin in a molding die cavity is usually disposed at a portion of the molding die corresponding to an end of the housing frame portion 422 opposite to an end having the light sources 410, 410. In this case, the resin injected in the molding die cavity through the injection gate is caused to flow into a cavity segment for the light conductor plate portion 421 through paths each provided between adjacent two grooves 425 thus generating a plurality of resin flows which meet and interfere with one another inside the cavity segment thereby forming what are called “weld lines”, and adverse effects are caused on the optical properties of the light conductor plate portion 421 thus formed.